Probe assemblies having therapeutic and/or diagnostic capabilities are being increasingly utilized by the medical community as an aid to treatment and/or diagnosis of intravascular and other organ ailments. In this regard, U.S. Pat. No. 5,115,814 discloses an intravascular ultrasonic imaging assembly with a distally located imaging element that is positionable relative to intravascular sites. Operation of the imaging element in conjunction with associated electronic image recovery components generates visible images that aid an attending physician in his or her treatment of a patient's vascular ailments. In particular, a physician may view in real (or essentially near real) time intravascular images generated by the ultrasonic imaging probe element to locate and identify intravascular abnormalities that may be present and thereby prescribe the appropriate treatment and/or therapy.
The need to accurately position a distally located operative imaging element relative to an intravascular site using any therapeutic and/or diagnostic probe assembly is important so that the attending physician can confidently determine the location of any abnormalities within the patient's intravascular system. Accurate intravascular position information for the imaging assembly will also enable the physician to later replicate the same positions for subsequent therapeutic and/or diagnostic procedures, e.g., to enable the physician to administer a prescribed treatment regimen over time and/or to later monitor the effects of earlier therapeutic procedures.
By using computer-assisted reconstruction algorithms, current ultrasonic imaging systems enable physicians to view a representation of the patient's interior intravascular structures in both two and three dimensions (i.e., so-called three dimensional or longitudinal view reconstruction). To this end, image reconstruction algorithms employ data-averaging techniques which assume the intravascular structure between an adjacent pair of data samples is an average of each such data sample, i.e., the algorithms use graphical "fill in" techniques to depict a selected section of a patient's vascular system under investigation. Of course, if data samples are not sufficiently closely spaced, lesions and/or other vessel abnormalities may go undetected, since they might lie between a pair of data samples and thereby be "masked" by the image reconstruction algorithms.
As such, current reconstruction algorithms depend upon the ability to obtain and process very precisely longitudinally separated data samples of a section of a patient's vascular system under investigation. To this end, automated longitudinal translation of a distally located ultrasound imaging element is often employed to ensure the data samples are precisely spaced. For example, U.S. Pat. No. 5,485,486 discloses an imaging system in which an ultrasound imaging transducer is mounted on a distal tip of a rotating cable extending through a lumen of a catheter placed in a patient's vascular system, wherein the distal tip of the rotating cable is translated longitudinally at a precise constant rate through the use of a longitudinal translation assembly. In particular, the longitudinal translation assembly enables a series of precisely separated data samples to be obtained thereby minimizing (if not eliminating) distorted and/or inaccurate reconstructions of the ultrasonically scanned vessel section, i.e., since a greater number of more closely spaced data samples can reliably be obtained. Further, a precisely controlled pullback speed makes it possible to take measurements in a longitudinal direction, e.g., a lesion length.
Notably, a main advantage of this automated pullback assembly is that it can be operated in a "hands-off" manner which allows the physician to devote his or her attention entirely to the real-time images with the assurance that all sections of the vessel are displayed. On the other hand, the disclosed system is relatively large and can be cumbersome for a physician to set up, in part because the longitudinal translation assembly and a rotary drive motor used to rotate the imaging cable must each be wrapped in separate sterile drapes (i.e., plastic bags) in order to perform the imaging procedure.
U.S. Pat. No. 5,361,768 discloses an improved system over that disclosed in U.S. Pat. No. 5,485,486, in that a single drive unit provides the requisite longitudinal and rotational translation of the imaging cable. However, the respective rotational and longitudinal movement of the cable is still provided by separate motors, thereby making the "combined" drive unit larger and heavier than either of the previous separate units.
Thus, it remains desirable to provide a still further improved drive unit for both rotational and precisely controlled translational movement of an imaging cable in an ultrasonic catheter imaging system.